The invention relates to a display device comprising an electro-optical display medium between two supporting plates, a system of picture elements arranged in rows and columns, with each picture element being formed by picture electrodes arranged on the facing surfaces of the supporting plates, and a system of row and column electrodes for presenting selection and data signals by means of which a range of voltages dependent on the electro-optical display medium can be presented across the picture elements for the purpose of picture display.
The invention also relates to a method of driving such a display device.
A display device of this type is suitable for displaying alphanumerical information and video information by means of passive electro-optical display media such as liquid crystals, electrophoretic suspensions and electrochromic materials.
A display device of the type described in the opening paragraph is known from Netherlands Patent Application No. 8502663 laid open to public inspection, in the name of the Applicant. In the device shown in this Application diodes are used as non-linear switching elements in an active matrix, namely two diodes per picture element. Two successive rows of picture elements each time have one row electrode in common. The drive mode is such that in television applications (for example, with a drive mode in accordance with the PAL or NTSC system) the information of two successive even and odd lines is presented across each picture element at an alternating polarity and at the field frequency. The information of a picture element is therefore determined by the average signal of two successive even and odd lines. Since each time two rows of picture electrodes are simultaneously written, because two successive rows each time have one row electrode in common, such a device provides little flexibility as regards the choice of colour filters to be used. In practice, this choice is limited to strip-shaped colour filters.
U.S. patent application Ser. No. 208,185, filed Jun. 16, 1988 in the name of the Applicant describes a picture display device of the type mentioned in the opening paragraph in which the row electrodes are not common and in which the rows of picture elements are separately driven without the omission of common row electrodes leading to an increase of the number of connections.
This ensures a considerable freedom regarding the colour filters to be used. This is possible by giving the picture elements a given adjustment per row by charging or discharging the capacitances associated with these picture elements after first having discharged or charged them too far (whether or not accurately).
In the said Patent Application this is realised by applying, prior to selection, an auxiliary voltage across the picture elements beyond or on the limit of the voltage range to be used for picture display, for example, by means of an auxiliary voltage (reference voltage) or a reset voltage.
In a preferred embodiment of the device described in said Patent Application a Zener diode is arranged between a picture element and a row or column electrode. When using such a device, the breakdown behaviour of the Zener diodes used also determines the operating voltages to be used, and the minimum Zener breakdown voltage limits the number of electro-optical media to be used. Moreover, Zener diodes in the technology employed in circuits for liquid crystal devices (amorphous silicon, polycrystalline silicon) are difficult to manufacture in a reproducible manner. It is an object of the invention to meet these drawbacks by providing an alternative solution.